To set things straight: My question is fair. I'm not criticizing the LMDE's crew's work in any way. So please, nobody gets mad here.

I've switched from the regular Mint to Mint Debian because I had to squeeze out every ounce of performance. By eliminating Ubuntu's intermediary. And I'm a happy LMDE user (apart from an annoying NVidia Twinview problem I hope which will be fixed in UP5).

Now, I have a colleague here who's using Debian (Test) directly. With the same software: Various Samba, Java stuff, Chrome, XFCE desktop and NVidia Twinview. Apparently without hacking his way in whatsoever.

I would just say that Update Pack are increasing stability and offering new softwares in the same time compare to Debian Testing who can be a little bit more touchy to use. That's the big advantage of LMDE. You have some mint stuff but the difference with a pure Debian is not big. The proof is that you can use Debian repo directly. It is maybe easier to use & configure LMDE over Debian for a beginner.

Right now it's probably not a fair comparison because Testing is frozen and not likely to break. But when testing is working like it should, things can break and the user have no idea how to fix them. UPs provide information along with each update, as well as solutions to problems that might arise.

Also, it's great for someone who doesn't want updates EVERY DAY. (For me, it gets old fast!)